Impaired scaling of preparatory postural responses to repeated balance perturbations in Parkinsonian patients with comorbid white matter disease.

BACKGROUND: Postural instability may result from altered sequencing of automatic motor programs for anticipatory postural corrections and/or impaired motor learning in Parkinson Disease (PD) patients. Comorbid white matter disease is a major determinant of axial motor impairment, leading to poorer stability than nigrostriatal dopaminergic denervation per se. OBJECTIVE: To assess differences in anticipatory control of postural stability function between subjects affected by PD with comorbid leukoaraiosis (LPD), idiopathic Parkinson disease (IPD) and elderly healthy subjects (EHS) as control group. METHODS: Eight patients with IPD, eight patients with LPD and eight age/weight matched elderly healthy subjects (EHS) were tested in standing position by measuring the Center of Pressure (CoP) along the anteroposterior axis (CoP-Y) while subjects were expecting three repeated backward surface translation. RESULTS: LPD patients positioned the CoP-Y significantly backward while waiting for the second and third platform translations, with respect to their COP-Y position in preparation for the first translation. The IPD and EHS showed no significant differences in the COP-Y position among the repeated perturbation trials. CONCLUSIONS: LPD patients show inability to rescale an effective preparatory postural pattern to known, repeated postural perturbations suggesting impaired sensory-motor strategies in anticipating perturbations. Anticipatory postural patterns remain effective in IPD patients.